[1.6.x] Fixed #14786 -- Fixed get_db_prep_lookup calling get_prep_value twice if prepared is False.

Thanks homm for the report and Aramgutang and lrekucki for work on
the patch.

Backport of f19a3669b8 from master

1 files changed, 1 insertions, 0 deletions

diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 0b5e7d4782..e2f8c6c48e 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -385,6 +385,7 @@ class Field(object):
         """
         if not prepared:
             value = self.get_prep_lookup(lookup_type, value)
+            prepared = True
         if hasattr(value, 'get_compiler'):
             value = value.get_compiler(connection=connection)
         if hasattr(value, 'as_sql') or hasattr(value, '_as_sql'):